Method of digital trunked communication system fast call setup

ABSTRACT

The present invention discloses a method of fast call setup in digital trunking communication system, including: the terminal user initiating a PTT call; the base station receiving said PTT call request, assigning channel resource for the call, establishing forward service channel according to the distribution of channel, transmitting an empty frame on the forward service channel and at the same time transmitting an extended channel assignment message to specify the service channel assigned for the terminal; after receiving the extended channel assignment message, the terminal user opening the receiver to track and acquire the forward service channel, and at the same time transmitting one or more prefix-frame on the reverse service channel or reverse pilot channel; the base station or the terminal performing the operation of acquisition of service channel, if the acquisition succeeds, the call setup is successful, if the acquisition fails, the call setup is failed and enters release flow. The method of the present invention adopts a mode of overlapping of signaling handshake and channel acquisition, so as to advance the signaling handshake, reduce call accessing time, and realize fast call setup.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the priority of PCT applicationPCT/CN2004/001568 titled “A METHOD OF DIGITAL TRUNKED COMMUNICATIONSYSTEM FAST CALL SETUP”, the teachings and disclosure of which arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a method of establishing call in mobilecommunication system, especially relates to a method of fast call setupin mobile trunking communication system based on CDMA (Code DivisionMultiplex Access) standard.

BACKGROUND ART

Under the promotion of the increasingly diverse social demands, themobile communication technology has developed from analog communicationsystem to the current widely used second generation mobile communicationsystem and 2.5 generation mobile communication system, and until thethird generation mobile communication system which will be employed in awide range in the near future. The development of mobile communicationtechnology not only meets the demands of people on voice service, butalso effectively meets the demands for the value-added servicesincluding the video, audio and interaction of real-time multimediaservices, thereby the mobile communication system plays a more and moreimportant role in people's life and work. Among the above, the trunkingcommunication has increasingly become an indispensable service, thedigital trunking system is an important branch of the mobilecommunication system, and is a special mobile communication system formultiple users sharing and dynamically utilizing a group of wirelesschannels.

The method of realizing trunking services in CDMA2000 system includestwo types: the group call and the private call, which are importantservice features of the trunking system. The group call means that asingle user can talk with all the other users in the groupsimultaneously in a permitted time. When one user is talking, all theother users in the group must listen to him. Once a user in the grouppushes the PPT (Push To Talk) button, other users in the group whosepriority level is same with that of the user pushing the PPT button cannot break in but only wait till the talk is finished. The private callis one-to-one call between users, a user can talk to the one who he isintended to talk in the group without being heard by other users in thegroup. The trunking system based on CDMA standard adopts grouping datachannels for trunking call service, i.e. to realize fast call setup byadopting Ethernet transmission, rather than the traditional circuitexchange in circuit domain. In order to meet the needs of trunking groupcall and private call, the trunking system based on CDMA standard adoptsthe method of fast call access. The features of the truckingcommunication system based on CDMA standard lie in that it adoptssemiduplex communication mode, can realize a fast access and supportsthe group call, i.e. the calling mode of one-to-multi-users. In trunkingcommunication, the users in the group are required to share the forwardchannel within a region. When users in the group are to call or talk,they only need to press PTT button, then they are able to talk withother users in the group. This type of PTT service is widely applied tointercommunication system and trunking system, providing command anddispatch functions for group users, such as police, fire-fighting,transportation and communication, air station and aviation, constructionsite, large-scale gathering, and military dispatching etc. Withadvancement of society, increase of population mobility, and fastdevelopment of mobile communication technology, the range of personalcommunication is becoming wider and wider. The application of trunkingservice also gradually turns to the individuals, for example, it may beapplied in the chat among fashionable young peoples or smallcommunities, and communications between family members. The trunkingcommunication system based on CDMA standard can attract not only newindividual users, but also some professional users for the operators.

The most important character of the trunking communication is that itrequires short accessing time and quick acquisition of channel. But thetraditional CDMA system adopts the method of serial acquisition. Thebase station subsystem sends out the Extended Channel Assignment Message(ECAM), then sends empty frames to terminal user on the service channelassigned; the terminal user processes the ECAM message, then turns tothe forward service channel, and transmits the prefix-frame on thereverse channel after receiving at least two continuous valid emptyframes; after acquiring the reverse channel, the base station subsystemsends Base Station Acknowledge Order (BSAckOrder) message to theterminal user, and points out in the Base Station Acknowledge Ordermessage that the message needs to be verified; the terminal userresponses by sending message of Terminal Acknowledge Order (MSACKOrder),and points out whether the message needs to be verified by the basestation. The above procedures are on the premise that the terminalacquires the forward channel, if the terminal does not acquire theforward channel, it will not send the reverse prefix-frame. However,this type of serial procedure takes a long time for acquisition, and thesignaling handshake can only be proceed after the whole acquisitionprocess is finished. Moreover, the requirement of fast call setup ingroup call can not be satisfied due to the added time for establishingcall. In addition, since trunking communication is mainly applied toemergent dispatch, such as the marine emergency, military dispatching,public security command and rush-to-danger dispatching, which are urgentand have high requirement on time, the call establishing time by thetraditional cellular mobile communication system can only meet therequirements of common users, but not the trunking users' requirementson fast response. In order to meet the fast response requirement of thetrunking communication, the ordinary call establishing procedure must bereformed to reduce the acquisition time, thereby meeting the fast callsetup requirement of the digital trunking communication system. Atpresent, there is still no effective method of fast call setup in thedigital trunking system based on CDMA technology.

SUMMARY OF THE INVENTION

The present invention aims to provide a method of fast call setup indigital trunking communication system, so as to overcome the shortcomingof the existing technology that the digital trunking system based onCDMA standard can not realize the function of fast access and call,thereby realizing fast call setup.

In order to realize the above aims, the present invention provides amethod of fast call setup in digital trunking communication system,including the following steps of:

Step 1, a terminal user initiating a PTT call;

Step 2, after receiving the PTT call request, a base station assigningchannel resource for the call, establishing forward service channelaccording to the distribution of channel, transmitting empty frame onthe forward service channel, and at the same time transmitting extendedchannel assignment message to specify the service channel assigned forthe terminal;

Step 3, after receiving the extended channel assignment message, theterminal user opening a receiver to track and acquire the forwardservice channel, and at the same time transmitting one or moreprefix-frames on reverse service channel or reverse pilot channel;

Step 4, the base station or the terminal performing the operation ofacquiring service channel, if the acquisition succeeds, the call setupis successful, if the acquisition fails, the call setup is failed, andenter into release flow.

In the operation of acquiring service channel in step 4, if the basestation acquires the reverse service channel first, said operation ofacquiring service channel includes the following steps of:

step 4a, the base station transmitting a base station acknowledge order(BSAckOrder) message to the terminal, and requesting the terminal toreturn a verification;

step 4b, if the base station receives the message of acknowledge order(MSAckOrder) from the terminal, the acquisition of service channel isaccomplished, the base station and the terminal access into the servicechannel, and the call setup is successful; if the base station does notreceive the message of acknowledge order (MSAckOrder) from the terminal,the acquisition of service channel is failed, the call setup is failed,and enter into the release flow.

In the operation of acquiring service channel in step 4, if the basestation acquires the forward service channel first, said operation ofacquiring service channel includes the following steps of:

Step 4a′, the terminal transmitting terminal message of acknowledgeorder (MSAckOrder) to the base station, and requesting the base stationto respond;

step 4b′, if the terminal receives the BSAckOrder message from the basestation, the acquisition of service channel is accomplished, the basestation and the terminal access into the service channel, and the callsetup is successful; if the terminal does not receive the BSAckOrdermessage from the base station, the acquisition of service channel isfailed, the call setup is failed, and enter into the release flow.

In the operation of acquiring service channel in step 4, if the basestation and the terminal acquire corresponding reverse service channeland forward service channel simultaneously, the base station and theterminal mutually transmit verification to each other simultaneously,and respond to the verification mutually; if the base station and theterminal receive the verification message from each other respectively,the acquisition of service channel is accomplished, the base station andthe terminal access into the service channel, and the call setup issuccessful.

The method of the present invention adopts a mode of overlapping ofsignaling handshake and channel acquisition, so as to advance thesignaling handshake, reduce call accessing time, and realize the methodof fast call setup. During the process of acquisition and access, thebase station does not take the traditional method of sending emptyframes, but adopts the way of sending the BSAckOrder signal directly inthe acquisition process. After the mobile station receiving twocontinuous valid frames and the BSAckOrder message, it does not send theprefix-frame, but sends the MSAckOrder to response. By operating thesignaling handshake in advance, the procedures of service channelacquisition and signaling handshake are operated simultaneously, so thatthe accessing time of trunking users is saved, and the shortcomings ofthe CDMA system that the accessing time is too long and can not meet therequirements of trucking service are overcome.

The technical schemes of the present invention is further describedbelow in combination with the attached drawings and detailedembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flowchart of the method of fast call setup in digital trunkingsystem of the present invention.

FIG. 2 is schematic view of message interaction according to anembodiment of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention puts forward a method of parallel acquisition torealize the fast access of the trunking group call and the trunkingprivate call. When a user presses PTT button to begin a PTT group callor a PTT private call, the base station of the BSS (Base StationSubsystem) receives the calling request, and assigns the channelresources for this call. The BSS establishes a forward service channelaccording to the assignment of the channel, and sends out an extendedchannel assignment message (ECAM) in the air to specify the servicechannel assigned for the terminal, at the same time, it sends out emptyframes on the forward service channel. After the terminal receiving theECAM, it turns on the receiver to trace and acquire the forward servicechannel, and at the same time, sends out a plurality of prefix-frames onthe backward service channel or on the reverse pilot channel directly,without necessity to send the prefix-frames after receiving twocontinuous valid frames. At this moment, the base station and theterminal will send out the empty frames and the prefix-framesrespectively. In the acquisition process, it is not always that the basestation acquires the reverse service frames first, it is possible thatthe terminal acquires the forward service frames first. If the basestation successfully acquires the frames prior to the terminal, ittransmits the verification message BSAckOrder to the terminal first, andrequires the terminal to verify the message, then the terminal feedsback reverse message MSAckOrder to the base station for verificationafter it receives the verification message from the base station; if theterminal successfully acquires the frames first, it transmits theverification message MSAckOrder to the base station subsystem first, andrequires the base station to verify the message, then the base stationfeeds back the verification message BSAckOrder to the terminal forverification after it receives the verification message from theterminal. If the base station and the terminal acquire the framessimultaneously, it is possible that they will send out the verificationssimultaneously, and response to the verifications mutually, which willslow down the process. But this situation rarely happens. As such, thewhole procedure of acquiring service channel is accomplished, which isoperated in parallel.

The present invention is applied in the trunking system based on CDMAstandard to realize the fast call setup. It overcomes the disadvantageof time-consuming of the traditional serial acquisition and channelmessage verification mechanism of the one-way service, and adopts themethod of parallel channel acquisition to reduce the time for user callaccessing.

The detailed flow is shown in FIG. 1:

Step 1, the terminal user pushes the PTT button to initiate a PTT call,and the PTT call can be group call or private call;

Step 2, the base station receives the call request, assigns channelresource, establishes forward service channel, and transmits emptyframes on the service channel; in the meantime, the base stationtransmits extended channel assignment message ECAM to the terminal;

Step 3, the terminal receives the ECAM, then opens the receiver to trackand acquire the forward service channel, and at the same time transmitsprefix-frame on reverse service channel or reverse pilot channel;

Step 4, whether the base station acquires the reverse service channelfirst? If yes, turn to step 4a, if not, turn to step 4′;

Step 4a, the base station transmits BSAckOrder message to the terminal,and requires the terminal to response, then it waits for the responsefrom the terminal;

Step 4b, whether the base station receives the acknowledge message fromthe terminal? If yes, turn to step 5; if not, turn to step 5′;

Step 4′, whether the terminal acquires the forward service channelfirst? If yes, turn to step 4a′, if not, turn to step 4a″;

Step 4a′, the terminal sends the MSAckOrder to the base station, andrequests the base station to respond; the terminal waits for theresponse from the base station;

Step 4b′, whether the terminal receives the acknowledge message from thebase station? If yes, turn to step 5; if not, turn to step 5′;

Step 4a″, the base station and the terminal acquire the service channelsimultaneously, the base station and the terminal send verificationsmutually, and wait for the verification returned from each other;

Step 4b″, whether the verifications return? If yes, turn to step 5; ifnot, turn to step 5′;

Step 5, the service channel acquisition is accomplished, and the call issuccessful.

Step 5′, the service channel acquisition is failed, and the call isfailed.

FIG. 2 is the schematic view of message interaction according to theembodiment of the present invention that the base station successfullyacquires reverse service channel first. The process of messageinteraction is as follows:

the terminal user pushes the PTT button to launch a group call requestor a private call request to the base station (201);

the base station receives the call request for the group call or theprivate call, and judges whether it is a group call or a private callaccording to the SO (Service Option) of the call, the base stationassigns channel resource and physical resource for the call, establishesthe forward service channel based on the assigned resources, and sendsempty frame on the forward service channel to the terminal;

the base station constructs the extended channel assignment message ECAMbased on the calling type and the channel resource assigned, thentransmits the channel assignment message on the paging channel to theterminal (202);

the terminal receives the extended channel assignment message ECAM fromthe base station, gets the channel attributes of the call, traces andacquires the forward service channel according to the channelattributes, and at the same time the terminal opens the transmitter totransmit the prefix-frame on the reverse service channel or the reversepilot channel (203);

if the terminal is an IS95 terminal and the radio configuration is RC1or RC2, the terminal transmits the prefix-frame on the reverse servicechannel;

if the terminal is a CDMA2000 terminal and the radio configuration isRC3, the terminal transmits the prefix-frame on the reverse pilotchannel;

Up to this point, the terminal and the base station start to enter thestage of parallel channel acquisition, if the base station acquires thereverse service channel successfully, it sends the BSAckOrder message tothe terminal and requires the terminal to verify the message; in themeantime, the base station sets timer in the LAC layer (204).

If such problem occurs that the base station does not receive theverification message from the terminal within the scope of the timer,then the channel acquisition fails, the call setup is failed, and entersrelease flow;

if the terminal receives the BSAckOrder message from the base station,and the message field ACK_REQ is 1, which indicates that the messagefrom the base station needs a reverse verification, then the terminalsends MSAckOrder to the base station for verification (205), and if theMSAckOrder message does not need to be verified, its ACK_REQ is 0;

the base station receives the MSAckOrder message from the terminal, thenthe service channel acquisition is accomplished, the base station andthe terminal access into the service channel, and the call setup issuccessful (206).

If the terminal receives two successive valid frames, but does notreceive the BSAckOrder message from the base station, it means that theterminal acquires the channel prior to the base station, thereuponentering the flow that the terminal acquires the channel first, theprocessing manner is same with that of the base station: sendingMSAckOrder message which requires for verification, and then setting thetimer in LAC layer.

The trunking communication system based on CDMA standard adopts thetechnology of the third generation mobile communication system, having alarge developing space in terms of technology and service; the method ofthe present invention is based on the mature CDMA technology, it onlymodifies the application of the air interface rather than changing thephysical mechanism of the air interface. The present invention adoptsthe method of parallel acquisition, thereby speeding up the call setup.The present invention not only satisfies the requirement on time for thefast call setup in the trunking system based on CDMA standard, but alsois valuable in accelerating the call setup in the common CDMA2000system.

Finally, it needs to be pointed out that the above embodiments are forillustrating the technical schemes of the present invention, they arenot limitations to the present invention. Although the present inventionis described in detail by referring to the above preferred embodiments,people skilled in the art should understand that amendments and equalreplacements can be made to the technical schemes of the presentinvention under the spirit and scope of the technical schemes of thepresent invention, and all such amendments and equal replacements shouldbe covered in the scope of the claims of the present invention.

1. A method of fast call setup in digital trunking communication system,comprising the steps of: 1) initiating, by a terminal, a request for apush-to-talk (PTT) call; 2) receiving, by a base station, the requestfor the PTT call; assigning by the base station a channel resource forthe PTT call, in order to establish by the base station a forwardservice channel in accord with a distribution of channels, transmittingat a same time by the base station: one or more empty frames on theforward service channel; and an extended channel assignment message tospecify a service channel assigned for the terminal; 3) receiving by theterminal the extended channel assignment message, then at the same time:opening by the terminal a receiver to track and acquire the forwardservice channel; and transmitting by the terminal one or moreprefix-frames; and 4) attempting by the base station and the terminal toacquire service channels simultaneously, so as to complete the callsetup, wherein if the attempting to acquire the service channels fails,the channel resource for the PTT call is released.
 2. The method of fastcall setup in digital trunking communication system of claim 1, wherein,in the step 4) of attempting by the base station and the terminal toacquire the service channels simultaneously, if the base stationacquires a reverse service channel first, the method further comprisesthe steps of: 4a) transmitting by the base station a base stationacknowledge order (BSAckOrder) message to the terminal and a request bythe base station for the terminal to return a verification message; and4b) receiving by the base station a message of acknowledge order(MSAckOrder) from the terminal, for access by the base station and theterminal into the service channels respectively, in order for the callsetup to be completed, wherein if receipt by the base station of themessage of acknowledge order (MSAckOrder) from the terminal fails, thechannel resource for the PTT call is released.
 3. The method of fastcall setup in digital trunking communication system of claim 2, wherein:step 4a) further comprises the base station sending the BSAckOrdermessage to the terminal, and at the same time, the base station settingand beginning a timer in a LAC layer; step 4b) further comprises, if thebase station receives the message of acknowledge order (MSAckOrder) fromthe terminal within the timing range of the timer, acquiring the servicechannels by the base station and the terminal, wherein both the basestation and the terminal access into the service channels, in order tocomplete the call setup, wherein if the base station does not receivethe message of acknowledge order (MSAckOrder) from the terminal withinthe timing range of the timer, the call setup is failed, and the channelresource for the PTT call is released.
 4. The method of fast call setupin digital trunking communication system of claim 1, wherein, in thestep 4) of attempting by the base station and the terminal to acquirethe service channels simultaneously, if the terminal acquires theforward service channel first, the method further comprises the stepsof: 4a′) sending by the terminal a terminal message of acknowledge order(MSAckOrder) to the base station and a request by the terminal the basestation to respond; and 4b′) if receiving by the terminal a base stationacknowledge order (BSAckOrder) message, to access by the base stationand the terminal into the service channels respectively, in order forthe call setup to be completed, wherein if receipt by the terminal theBSAckOrder message from the base station fails, then the call setup isfailed and the channel resource for the PTT call is released.
 5. Themethod of fast call setup in digital trunking communication system ofclaim 4, wherein: step 4a′) further comprises the terminal sending theterminal message of acknowledge order (MSAckOrder) to the base station,and at the same time, the terminal setting and beginning a timer in aLAC layer; step 4b′) further comprises, if the terminal receives themessage of acknowledge order (BSAckOrder) from the base station withinthe timing range of the timer, acquiring the service channels by thebase station and the terminal, wherein both the base station and theterminal access into the service channels, in order to complete the callsetup, wherein if the terminal does not receive the BSAckOrder messagefrom the base station within the timing range of the timer, the callestablishment is failed, and the channel resource for the PTT call isreleased.
 6. The method of fast call setup in digital trunkingcommunication system of claim 1, wherein, in the step 4) of attemptingby the base station and the terminal to acquire the service channelssimultaneously, if the base station and the terminal acquire thecorresponding reverse service channel and forward service channelsimultaneously, the method further comprises: mutually andsimultaneously sending, by the base station and the terminalverification messages; and responding to the verification messages fromthe other side respectively, wherein when the base station and theterminal receive the responses transmitted by the other siderespectively, the base station and the terminal access into the servicechannels respectively, and the call setup is completed.
 7. The method offast call setup in digital trunking communication system of claim 1,wherein, in the step 3) of transmitting by the terminal one or moreprefix-frames: if the terminal is an IS95 terminal and the radioconfiguration is RC1 or RC2, the terminal sends the one or moreprefix-frames on a reverse service channel; and if the terminal is aCDMA2000 terminal and the radio configuration is RC3, the terminal sendsthe one or more prefix-frames on a reverse pilot channel.
 8. The methodof fast call setup in digital trunking communication system of claim 1,wherein, in the step 1), the request for the PTT call is one of a groupcall request and a private call request.